High pressure electric discharge device having a fill including vanadium



Y 1957 J. F. WAYMOUTH ETAL 3,331,982

HvlGH PRESSURE ELECTRIC DISCHARGE DEVICE HAVIN A FILL INCLUDING VANADIUMFiled Oct. 20, 1964 FILL INCLUDES MERCURY HALOGEN VANADIUM JOHN FWAYMOUTH FREDERIC KOURY INVENTOR 3 AT ORNEY United States Fatent C)3,331,982 HIGH PRESSURE ELECTRIC DISCHARGE DEVICE HAVING A FILLINCLUDING VANADIUM John F. Waymouth, Marblehead, and Frederic Koury,

Lexington, Mass, assignors to Sylvania Electric Products Inc., acorporation of Delaware Filed Oct. 20, 1964, Ser. No. 405,087 9 Claims.(Cl. 313-225) This invention relates to high pressure electric dischargedevices and particularly to the production of white light from suchdevices.

High pressure electric discharge devices are well known to the art,however, white light with high red rendition has not been obtained fromtheir practical commercial applications. Most commercial high pressureelectric discharge devices contain mercury vapor and the dischargeproduced is only the typical mercury discharge consisting of discrete,separate wavelengths, generally called lines. Almost all of the radationis contained in the blue region together wth a line in the green and aline in the yellow. Hence when a conventional high-pressure mercurydischarge device illuminates a red object, particularly one reflectinglight only in the range of 6000 to 6800 A., the object appears black.

Attempts have been made by the art to obviate this problem and among thesuggested modifications have been the inclusion in the mercury arcstream of various metallic elements which emit radiation at wavelengthsdifferent than mercury emission, so that lamps having such inclusionswill produce radiations resulting from a combination of mercury linestogether with lines of the metallic additions. Typical of the inclusionshave been the addition of zinc, cadmium or sodium metals. Although suchadditions did add other lines to the spectrum and improve the colorrendition, still only a series of separate and discrete lines weregenerally present. Little, if any, color selectivity was provided.

Another suggested modification was the color-improved mercury vaporlamps wherein the inner surface of the outer bulbous envelopes wascoated with fluorescent phosphors which converted some of the invisibleultraviolet arc radiation into visible light of a red-orange color.Although the mixture of the red-orange together with the blue-green ofthe mercury produced some change in color, there was a loss ofefficiency in the lamp because the phosphor absorbed some of the visibleradiation from the arc. Furthermore, phosphors coating failed to solvethe real problem which is the lack of the desired light emission in theradiation of the discharge itself.

We have discovered that light of color other than the bluish hue can beobtained from a high pressure electric discharge if certain materialsare used as fills in the arc tube. Such fills are the conventionalmercury together with a halogen, preferably iodine and except fluorine,either as the elements, the corresponding compounds or mixtures thereof.Included in this fill is vanadium added either as the element or thecorresponding halide, iodides being preferred or mixtures of the elementand the iodide compound. Through this combination, certain new andunexpected results occur. A beautiful orchid color emission is produced.Notably, certain ratios of iodine atoms to mercury atoms must bemaintained, elsewise maximum light emission will not be realized.

The radiation which is produced from are tubes using fills includingvanadium is a spectrum containing all colors and many spectral lines,the spacing between the lines averaging less than about A. The emissionhas a broad base continuous spectrum when measured on an instrument ofmoderate resolution with a large number of broad peaks, particularly inthe red, 6000 to 6400 A., region. Because of the presence of mercury,the typical mercury lines at 4048, 4348, 5461, 5770 and 5790 A. will besuperimposed upon the spectrum. Included also is a number of peaks inthe red and green regions which accounts for the orchid emission. Ofcourse, the emission spectrum of any color modifying metals or otheradditions will be present when such metals are added. For example,thallium can be added for increased green emission and sodium forincreased yellow.

As we have indicated, the quantities of iodine and mercury must beclosely controlled to attain maximum efiiciency. We prefer to use aratio of iodine atoms to mercury atoms of about 0.5, although it ispossible to use ratios between 0.025 to 0.85; the preferred range ofratios being between 0.025 and 0.65. Irrespective of whether the mercuryis added as the metal or the corresponding iodide, its quantity shouldbe sufiicient to allow complete vaporization at normal operatingtemperatures of the arc tube and to form a restricted arc in the arctube.

Accordingly, the primary object of this invention is the production of acontinuous spectrum with high red rendition from high pressure electricdischarge devices.

A feature of this invention is the incorporation of mercury, either asthe metal or as the iodide, together with controlled quantities ofvanadium, also either as metal or as the iodide.

Many other objects, features and advantages of the present inventionwill become manifest to those conversant with the art upon makingreference to the detailed' description which follows and theaccompanying sheet of drawings in which preferred embodiments of a highpressure electric discharge device which emits a continuous spectrum areshown and described and wherein the principles of the present inventionare incorporated by way of illustrative examples.

Of these drawings:

FIGURE 1 is a spectral energy distribution graph illustrating theemission spectrum of vanadium-containing lamp.

FIGURE 2 is an elevational view partially in cross section of a highpressure electric discharge device illustrating the positioning of anelectric discharge are tube disposed within an outer bulbous envelope.

According to our invention we have discovered that arc tubes having afilling of a combination of certain materials can produce an orchidcolored light having a continuous spectrum without the necessity of acorrectional phosphor; the lamps having an efiiciency of to lumens perwatt and red rendition of 6 to 8%. In particular, when mercury andiodine, either as the individual elements or as the correspondingcompounds, are added to the arc tube in very specific atomic ratiostogether with specific quantities of vanadium, can be obtained. By acontinuum we mean an almost complete forest of spectral lines in theemission spectrum, appearing generally less than 5 A. apart andcontaining superimposed upon this forest, the typical mercury lines at4048, 4348, 5461, 5770 and 5790 A.

In lamps containing iodine and metals other than mercury, the arc tendsto be somewhat restricted. These problems have been remedied through theaddition of sodium atoms. Such atoms can be easily excited at therelatively low temperatures existing at the perimeters of the arc tube,that is nearer the wall. Hence the arc becomes more diffuse. Theoperating voltage is reduced because the energy can be dissipatedthrough a wide area throughout the entire arc tube rather than in anarrow zone between the electrodes. In our lamp containing vanadium,this sodium can be eliminated. Sodium additions, however, can makevaluable contributions to the color of the discharge and hence, may beincluded for this reason.

Referring to FIGURE 2, an elevational View of a high pressure electricdischarge device is shown. For clarity of presentation, the outerbulbous envelope and the base of the lamp are shown in phantom linessurrounding the are tube harness and the arc tube. The device, such asshown in the drawing, comprises an outer vitreous envelope or jacket 2of generally tubular form having a central bulbous portion 3. The jacketis provided at its end with a reentrant stem having a press seal throughwhich extend relatively stiff lead-in wires 6 and 7 connected at theirouter ends to the electrical contacts of the usual screw type base 8 andat their inner ends to the 'arc tube and the harness.

The are tube is generally made of quartz although other types of glassmay be used such as alumina glass or Vycor,

the latter being a glass of substantially pure silica. Sealed in the arctube 12 at the opposite ends thereof are main discharge electrodes'13and 14 which are supported on.

lead-in wires 4 and 5, respectively. Each main electrode comprises'acore portion which may be prepared of a suitable metal such as forexample molybdenum or tungsten. The prolongations of these lead-in wires4 and can be surrounded by molybdenum or tungsten wire helixes. Ifdesired and necessary, asmallsliver of a metal of loW work function,such as thorium, which in this case should be less than about 0.5 mg,can be disposed between the heliX and the core in each of the electrodesto reduce cathode drop. In some caseswhere it may be disadvantageous toadd the spectrum of thorium, thoriated-tungsten wire (containing about 2to 4% thorium by weight) can be used or, of course, the thorium can beeliminated entirely.

An auxiliary starting probe or electrode 18, generally prepared oftantalum or tungsten is provided at the base end of the arc tube 12adjacent the main electrode 14 and comprises an inwardly projecting endof another lead-in wire.

Each of the current lead-in wires described, have their ends welded tointermediate foil sections of molybdenum which are hermetically sealedwithin the pinched sealed portions of the arc tube. The foil sectionsare very thin, for exampleapproximately 0.0008 inch thick and go intotension without or scaling off when the heated arc tube cools.Relatively short molybdenum wires 23, 24 and 35 are welded in the outerends of the foil and serve to convey current to the various electrodesinside the arc tube 12.

Metal strips 45 and 46 are welded onto the lead-in wires 23 and 24respectively. A resistor 26 is welded to foil stripv 45 which in turn iswelded to the arc tube harness. The resistor may have a value of forexample, 40,000 ohms and serves to limit current to auxiliary electrode18 during normal starting of the lamp. Metal foil strip 46 is welded atone end to a piece of molybdenum foil sealed in the arc tube 12 which inturn is welded to main electrode 13 and 14. Metal foil strip 47 iswelded-to one end of leadin 35 and at the other end to the harness. Thepinched or flattened end portions of the arc tube 12 form a seal whichcan be of any desired width and can be made by flattening or compressingthe ends of the arc'tube 12 while they are heated.

A U-shaped internal wire supporting assembly or are tube harness servesto maintain the position of the arc tube 12 substantially coaxiallywithin the envelope 2. To support the arc tube 12 within the envelopestiff lead-in wire 6 is welded to the base 53 of the harness. Becausestiff lead-in wires 6 and 7 are connected to opposite sides of a powerline, they .must be insulated from each other, together with all membersassociated with each of them. Clamps 56 and 57 hold the arc tube 12 atthe end portions and are fixedly attached to legs 54 of the harness. Arod 57 bridges the free end of the U-shaped support wire 54 and isfixedly attached thereto for imparting stability to the structure. Thefree ends of theU-shaped wire 54 are also provided with a pair of metalsprings 60, 'frictionally engaging the. upper tubular portion of thelamp envelope 2. A heat shield 61 is disposed beneath the arc tube 12and above the resistor 26 to protect the resistor from any excessiveheat generated during lamp operation.

The are tube 12 is provided with. a filling of mercury which reaches apressure in the order of one half to several atmospheres during normallamp operation at temperatures of 450 to 700 C. We have found thatthrough the addition of iodine and/ or certain mercury iodides to themercury fill, the quantity of the latter can bereduced. Arc lengthismeasured as the distance between opposing tips of the main electrodes 13and 14. Although the amount of mercury added can be varied widely as wehave indicated, we prefer to add approximately 2.5 l0- to 4.1 10" gramatoms of mercury per centimeter of arc length. However, substantiallight emission can beobtained at filling pressures less than the abovestated limits. Furthermore, the continuum formation with the orchidcolor appears to be substantially independent of the amount of mercurymetal added and hence the quantity of the latter can be reduced whilelamp operation is still attained. As is conventional in the art, aquantity of rare gas such as helium, argon, neon, krypton or xenon at apressure of about 25 millimeters of mercury is added to facilitatestarting.

As we have indicated previously iodine must be added to the arc tubetogether with the vanadium to attain the formation of the continuum.About 0.5 atom of iodine should be added for every atom of mercuryirrespective of whether it is added as the element or the correspondingmercury compound; although this ratio may be varied in reasonabletolerances between 0.025 to 0.65 atom of iodide per atom of mercury. Thetolerance range is necessary since it is difficult, if not impossible,to produce lamps in production lines wherein the ratio of mercury toiodine is exactly 0.5. Within such tolerances, reasonable continuumformation is still evidenced. Itis quite important, to use materialswhich are as anhydrous as possible in thearc tube, since theincorporation of water tendsto make the discharge hard to start.

We have found that about 5.2 10-' to 1.6X 10- gram atoms per centimeterof arc length of vanadium should be added to the arc tube to attainemission such as shown in FIGURE 1. Below the lower limit, the emissionwill not be apparent because insufficient quantities. of metal arepresent and above the upper limit, the metals will condense upon the arctube and blacken it. The spectral energy distribution of the lamp asshown in FIGUREI is for a lamp containing vanadium and iodine. Theemission is an orchid or violet with string blue and red. In thespectrum,

the predominent lines are due to vanadium and a strong line at 5980 A.is because of sodium contamination. Evaluation of the spectrograms showsmany more lines in the vanadium spectrum than are evident in the figure,however, this is due to broad slits of the instrument on which thespectrum is recorded. Hence for practical description, the spectrum is acontinuum which is stronger in the red and blue regions than in thegreen.

As we have stated, it is sometimes desirable to add 5.25 10-' to 6.8 10-gram atoms of sodium, lithium,

potassium, rubidium and/or cesium per centimeter of arc length for colorcorrection. Moreover, without such metals, the are sometimes tends to beslightly unstable, a bit restricted and the voltage drop is sometimestoo high to operate the lamp on conventional ballasts. But when morethan the stated upper limit is used, the metal will condense upon thearc tube and blacken it. The metal may be either as the metal or thecorresponding iodide the latter being substituted for the metal on amole for mole basis.

Of course, as discussed previously, the addition of the sodium adds thecharacteristic sodium spectrum to the emission and increases thebrightness of the lamp somewhat and for that reason alone, it may beadvantageous.

The fabrication of theenvelope, sealing techniques and positioning ofthe electrodes in the high pressure electric discharge device accordingto our invention takes place in a manner quite similar to that known tothe art with conventional mercury lamps. And further, the mercury may beadded to the arc tube by techniques well known to the art. To preparethe arc tube, we pump down an envelope having a pair of electrodesdisposed at either end thereof, and spaced about 7 cm. from each other,through an exhaust tubulation extending from the surface of the envelopeand disposed in communication with the interior thereof. The envelope isthen electrically baked and filled with argon to flush out residualimpurities, it is quite important to eliminate or substantiallyeliminate hydrogen from the arc tube. Hydrogen is known to effect thestarting of mercury lamps adversely, but its effect appears to begreater in the lamps prepared according to our invention. The diificultywith hydrogen appears to be due to the formation of hydrogen iodidewhich has a much higher vapor pressure than any other iodide present. Webelieve that for every atom of hydrogen, that there is an extra atom ofiodine in the vapor state. Presence of the iodine in the vapor stateincreases the voltage which must be applied to the lamps for starting.Hence, not only must hydrogen be substantially eliminated from the gasesin the filling of the tube, but each and every part going into making upthe arc tube must be free of residual hydrogen impurities. For example,the electrodes can be baked at 600 to 800 C. for a few hours beforetheir use to eliminate hydrogen which might occur due to precessing.Furthermore, care should be exercised when sealing the electrodes intothe arc tube to prevent hydrogen-containing, combustion gases fromseeping in or becoming absorbed upon the surface.

The pump and fill procedure above described is usually repeated three tofour times and then an arc is struck between the electrodes while thereis a filling of argon gas. This operation of the arc removes anyresidual impurities from the electrodes and these contaminants can thenbe easily drawn from the system when the argon filling is pumped out. Wethen drop through the exhaust tube approximately 42 mg. of mercury, 7.4mg. grams of mercuric iodide, 2.5 mg. of vanadium, 1.6 mg. thalliumiodide and 6.5 mg. sodium iodide to an envelope having an arc length ofapproximately 6.4 centimeters. The are tube is then filled toatmospheric pressure with argon gas which is slowly leaked out until apressure of about 23 millimeters of mercury is obtained. Subsequently,the exhaust tubulation is tipped off and the envelope is sealed. Testingof the lamp indicates that while light is present, the emission of thelamp being in the order of 68 lumens per watt and having a 7% redrendition.

It is apparent that modifications and changes may be made within thescope of the instant invention. For example, up to 50% of scandium orthorium may be substituted on an atom for atom basis for the vanadiumatoms in order to modify the emission color and enhance the efiiciencyof the lamp and still obtain the continuous spectrum. It is ourintention, however, to be limited only by the scope of the appendedclaims.

As our invention we claim:

1. A high pressure electric discharge device comprising: an arc tubehaving sealed ends and electrodes disposed in said ends; means to conveyelectrical energy to each of said electrodes, whereby an arc can formtherebetween; mercury and vanadium atoms disposed in said are tube, saidmercury being in suflicient quantities to be completely vaporized atnormal operating temperatures of said are tube and to form a restrictedarc therein; atoms of at least one halogen selected from the groupconsisting of iodine,

chlorine, bromine disposed in said are tube, said halogen and saidmercury being present therein at an atomic ratio of halogen to mercurybetween 0.025 and 0.65 said vanadium atoms being present in the vaporstate, when said device is operating, in sufiicient quantities tocontribute to the spectrum of the arc.

2. The device according to claim 1 wherein iodine is the halogen.

3. The device according to claim 1 wherein up to 5 0% of the vanadium issubstituted by atoms of a metal selected from the group consisting ofscandium and thorium on an atom for atom basis.

4. A high pressure electric discharge device comprising: an arc tubehaving sealed ends and electrodes disposed in said ends, means to conveyelectrical energy to each of said electrodes, whereby an arc can formtherebetween; mercury and vanadium atoms disposed in said arc tube, saidmercury being in suflicient quantities to be completely vaporized atnormal operating temperatures of said are tube and to form a restrictedarc therein; atoms of at least one halogen selected from the groupconsisting of iodine, chlorine, bromine disposed in said are tube, saidhalogen and said mercury being present therein at an atomic ratio ofhalogen to mercury between 0.025 and 0.65; the atoms of vanadium beingpresent in quantities in the range of 5.2 10- to 1.6 10+ gram atoms percentimeter of arc length.

5. The device according to claim 4 wherein iodine is the halogen.

6. The device according to claim 4 wherein up to 50% of the vanadium issubstituted by atoms of a metal selected from the group consisting ofscandium and thorium on an atom for atom basis.

7. A high pressure electric discharge device comprising: an arc tubehaving electrodes sealed at either end thereof; means to convey currentto each of said electrodes whereby an arc can form therebetween; avaporizable fill of iodine, mercury and vanadium atoms, said iodine andmercury respectively being present in an atomic ratio between 0.025 and0.65, said mercury being present in sufiicient quantities to becompletely vaporized at normal operating temperatures of said arc tubeand to form a restricted arc therein; the atoms of vanadium beingpresent in the arc stream in sufficient quantities to produce acontinuous spectrum.

8. The device according to claim 5 wherein 5.25 10+ to 6.8 10 gram atomsof an alkali metal are added per centimeter of arc length.

9. The device according to claim 7 wherein said vanadium is present inquantities in the range of 5.2 10+ to 1.6 l()+ gram atoms per centimeterof arc length.

References Cited UNITED STATES PATENTS 3,022,437 2/1962 Cooper 313-222 X3,234,421 2/1966 Reiling 313-229 X 3,243,625 3/1966 Levine 313-92FOREIGN PATENTS 1,177,248 9/1964 Germany.

JAMES W. LAWRENCE, Primary Examiner. STANLEY D. SCHLOSSER, Examiner.

1. A HIGH PRESSURE ELECTRIC DISCHARGE DEVICE COMPRISING: AN ARC TUBEHAVING SEALED ENDS AND ELECTRODES DISPOSED IN SAID ENDS; MEANS TO CONVEYELECTRICAL ENERGY TO EACH OF SAID ELECTRODES, WHEREBY AN ARC CAN FORMTHEREBETWEEN; MERCURY AND VANADIUM ATOMS DISPOSED IN SAID ARC TUBE, SAIDMERCURY BEING IN SUFFICIENT QUANTITIES TO BE COMPLETELY VAPORIZED ATNORMAL OPERATING TEMPERATURES OF SAID ARC TUBE AND TO FORM A RESTRICTEDARC THEREIN; ATOMS OF AT LEAST ONE HALOGEN SELECTED FROM THE GROUPCONSISTING OF IODINE, CHLORINE, BROMINE DISPOSED IN SAID ARC TUBE, SAIDHALOGEN AND SAID MERCURY BEING PRESENT THEREIN AT AN ATOMIC RATIO OFHALOGEN TO MERCURY BETWEEN 0.025 AND 0.65 SAID VANADIUM ATOMS BEINGPRESENT IN THE VAPOR STATE, WHEN SAID DEVICE IS OPERATING, IN SUFFICIENTQUANTITIES TO CONTRIBUTE TO THE SPECTRUM OF THE ARC.